In further confirmation of the importance of the gut-brain axis, 18 Italian students at the University of Verona from ages 18 to 33 that took a freeze-dried mixture of four probiotics for six weeks experienced less depression, anger and fatigue compared to a control group of 15 that consumed a placebo. The positive effects continued, as discovered in follow-up testing three weeks later. The probiotics group also slept better. The probiotic bacteria blend of 4 billion colony-forming units included Lactobacillus fermentum, Lactobacillus rhamnosus, Lactobacillus plantarum and Bifidobacterium longum.